With the above assumptions, analyses similar to those for the amplitron were performed for three waveguide materials. The klystron power dissipation employed for these analyses is as follows: Collector 998.5 watts Circuit Loss 900.0 watts Beam Interception 155.0 watts Heater 60. 0 watts Results of these analyses are shown in Figure 6-30. A total of 22 configurations differing in waveguide material, waveguide design, converter type, converter conductivity and waveguide surface treatment were studied using the 18m subarray size. As the study progressed it became apparent that a waveguide thickness of 0. 020 in (0.5 mm) was a good compromise considering subarray size, structural stability, and weight. This dimension also is the thinnest known to have been fabricated to date. Figure 6-31 shows the results for a selection of candidates for the amplitron, and Figure 6-32 compares amplitron and 6 kW klystron results for an unshielded waveguide design. We see that deflections for the aluminum result in a power loss above one percent as the dimension exceeds 5m for the amplitron and near 15m for the polyimide material. There is a modest improvement for a shielded waveguide case. The klystron, due to its higher waste heat, produces greater deflection than the amplitron even though a large portion (at the collector) can be radiated at elevated temperature. The difficulty with the aluminum requirement for an extremely small subarray dimension of 5m (order of magnitude increase in control electronics cost relative to 15m) was circumvented by devising a segmented subarray concept in which 5m sections are suspended from the supporting structure as shown in Figure 6-33. There is a weight penalty for this elaboration that would not be needed for the composite materials, and there may be a temperature problem on the stringers that was not evaluated, tungsten, for example, may have to be used.
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